Stabilized mineral oil composition



Patented Apr. 9, 1940 PAET' STABILIZED MINERAL OIL COMPOSITION Everett W. Fuller, Woodbury, N. 3., assignor to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application February 1, 1939, Serial No. 253,990

9 Claims.

specifically related to the improvement or stabilization of such mineral oil fractions by the use of novel compounds, or a novel class of compounds, which when admixed with a viscous min- 10 er'al oil in minor proportions will prevent or delay undesirable changes taking place in the oil.

As is well known to those familiar with the art, substantially all the various fractions obtained from mineral oils and refined for their various uses are susceptible to oxidation. The susceptibility of an oil fraction to oxidation and the manner in which oxidation manifests itself within the oil varies with the type and degree of refinement to which the oilhas been subjected and with the conditions under which it is used or tested. In other Words, the products formed in an oil fraction as a result of oxidation and the degree to which they are formed depends upon the extent to which the various unstable constituents or constituents which may act as oxidation catalysts have been removed by refining operations, and'also upon the conditions of use.

A highly refined viscous oil, for example, which is one that. has been refined by treatment with fuming sulfuric acid or. other means or combinations such as A1013, solventsarid acids (or with an increase in acidic bodies tends to lowerjthe 45 dielectric strength of the oil and has other harmful effects which are undesirable. The acids are .corrosive to metals andthus reduce the useful life of the oils as lubricants or for other purposes in which they come in contact with metals, and the 50 acidic materials are also injurious in textile lubricants and inspray oils.

Moderately refined oils, that is, oils that have been refined by treatment with only moderate amounts of sulfuric acid, or other refiningagcnts,

55 tend to form relatively small amounts of acidic oxidation products as compared with highly refined oils, but they undergo material color de preciation and form considerable amounts of sludge. The changes taking place in these oils are appreciably accelerated by the presence of 5 metal catalysts such as copper. Suflicient acid is generally formed to cause some reduction-in the dielectric strength of these oils, but the principal objection to them is their tendency to deposit sludge which interferes with heat transfer 10 in transformers and turbines and also causes plugging of oil feed lines in lubricating systems. Solvent-refined oils in general, which .have

1 been prepared by treatment with selective s01- in that it is attended by substantial color depreciation and sludge formation. Acid formation 20 is usually greater than in the case of moderately acid-refined oils, but considerably less than with highly refined oils. Both sludge and acid formation lower their value for many purposes, such as electrical insulation, lubrication, etc.- Also, 501- 25 vent-refined oils have found extensive use as lubricants for internal combustion engines because of their high viscosityindex, but under the conditions of use encountered in crankcases such oils develop constituents which arecorrosive to- 30 ward certain metal bearings such as-the cadmiumsilver'bearings, etc., which'are' sometimes used.

It is to be understood that this classification of oils as highly refined, moderately refined" and solvent refined" is by no means limiting and that there can exist oils whose refining and blending has been such as to make them intermediate in properties between the types set up. Thus,

response to inhibitors may be said to depend en- 40 tirely upon the type of oxidation and end products of oxidation of an oil, which in turn depends largely upon the degree'of refining this oil has had. Further the degree of refining required to produce these types of oils varies with the crude source so that'any one refining proceduremay produce either a highly refined oil or a moderately refined oil, depending upon the crude source; Pennsylvania type oils, for example, require muchless refining to produce highly refined oils than the Coastal type of oils.

The use of oxidationinhibitors for the purpose of stabilizing a viscous mineral oil fraction against the deleterious efiects of oxidation dis-' cussed above is well known. Since the action of 5 these inhibiting materials is apparently catalytic, the problem of their development is a diflicult one and is evidently influenced to a large degree by the oxidizable constituents which are in the oil following a particular refining treatment. Thus a particular inhibitor or class of inhibitors may be efiective to stabilize a highly refined oil against acid formation while the same inhibitor may have no appreciable effect upon acid, color or sludge formation in a moderately refined oil and vice versa. This same inhibitor may or may not be efiective in inhibiting acid, sludge and color formation in a solvent-refined oil and may or may not be eflective to inhibit the corrosive action of a solvent-refined oil toward metals such, for example, as the various normally corrodod alloys typified by cadmium-silver bearings.

The present invention is particularly concerned with a class of compounds which have been found to be highly efifective as inhibitors of acid formation in highly refined oils. It is also concerned with the stabilization of moderately refined oils and the inhibition of alloy corrosion with solvent-refined oils, but in these latter two instances one specific compound of the class appears to exhibit outstanding superiority over the other tested member of the general group or class contemplated herein.

The invention is predicated upon the discovery that certain of the thio-aldehydes are highly effective in small amounts as inhibitors of acid formation in highly refined oils. Two specific :ompounds in the class, namely trithioformaldeayde and trithioacetaldehyde, were tested in this regard and both were shown to be highly effec- ;ive. In the moderately refined oil and the sol- Jent-refined oil, however, the trithioformaldecycle was not found to be of particular efl'ectiveless. This compound is only slightly soluble in nineral oil, however, and it is likely that this nay have been the major factor contributing to be relatively poor showing which it made on hese particular oil fractions. In this regard it vill be understood that my invention contemilates the use of a suitable solvent such as benzol r a solubilizing alcohol to facilitate admixture vi the inhibiting agent with the oil.

The thioaldehydes, contemplated herein as lntioxidants for viscous mineral oils, are best :nown in their tripolymeric form, such polymers Icing illustrated by trithioformaldehyde (CH2S)3 .nd trithioacetaldehyde (CH3'CHS)3. They may e prepared by reacting the corresponding aldelyde with hydrogen sulfide and hydrochloric vcid (Baumann, Berichte 23, 60). Other methds may also be used such as treating an aldeiyde with sodium thiosulfate in the presence of Cl (Schmidt, Berichte 40, 865).

The following examples illustrate the effective- .ess of the class of compounds and certain pecific members within the class contemplated erein as anti-oxidants for mineral oil fractions.

EXAMPLE I Highly refined oils The oil employed in this test was of the highly refined type used in transformers and me like which had been obtained from 8. Coastal istillate by successive treatments with 98 per ant sulfuric acid in the ratio of 40 lbs. per bbl. nd 103 percent oleum in the ratio of 180 lbs. per 91. followed by neutralization, washing, and ay percolation. The refined oil had a specific ravity of 0.871, a flash point of 310 F. and a modem Saybolt Universal viscosity of 69. seconds at 100 F.

The test used, known as the modified German 1 tar test, involved heating a 150 gram sample of the oil at a temperature of 120 C. while bubbling oxygen gas through the oil for a period of '70 hours. ucts thus formed was found (a) by extracting the oil with alcoholic soda, neutralizing the extract and then weighing the precipitated material, which is calculated as per cent acidic tar, and (b) by titrating the acids formed in' the oil with alcoholic KOH and expressing the result as the neutralization number (N. N.) which is the milligrams of KOH required to neutralize the acid in one gram of oil. The results of this test are listed in Table I below where oils A and A1 represent the oil alone, oil B indicates oil A with 0.05 per cent trithloformaldehyde and oil C indicates oil A1" with 0.10 per cent trithioacetaldehyde.

From the foregoing results it will be seen that both of the thioaldehydes tested are very eifective in minute quantities as inhibitors of acid formation in highly refined oils.

EXAMPLEII Moderately refined oil The oil used in this test was a moderately refined light turbine oil stock obtained from a blend of 92 per cent Mid-Continent distillate and 8 per cent Coastal distillate by treatment with 70 lbs. of 98 per cent sulfuric acid per bbl., followed by neutralization, washing and clay percolation. The refined oil had a specific gravity of 0.879, a flash point of 385 F. and S. U. viscosity of 152 seconds at 100 F.

In testing moderately refined oils of the turbine 011 type for deterioration under the influence of oxidation the so-called "Brown-Boveri turbine oil test was used. In this test a sample of oil is heated to a temperature of 110 C. in air for 72 hours with a piece of copper foil in the oil, the results observed being final color, and acidity, expressed as neutralization number (N. N.)

This oil, blended with 0.10 per cent trithioacetaldehyde, when subjected to the foregoing test showed a Lovibond color of 8 and a neutralization number of 0.05 as compared with the oil alone, which after subjection to the same test had a Lovibond color of 15 and a neutralization number of 0.07. As has been pointed out above, the trithioformaldehyde, probably because of its low solubility, was not shown by this test to be an effective anti-oxidant for moderately refined oil, and the results obtained are not given since improved results may be obtainable through the use of a solvent.

EXAMPLE III Solvent-refined oil The two illustrative thioformaldehydes described herein were also tested for their effect upon the corrosive action 'of solvent-refined motor oils toward alloys such, for exampla'as cad- The amount of acidic oxidation prod-' mium-silver bearings of the type normally corroded bysuch oils under conditions of use. The oil used was an S. A. E. motor oil obtained from a Pennsylvania mixed neutral residuum stock by solvent extraction with chlorex. It had a specific gravity of 0.872, a flash point of 435 F. and an S. U. viscosity of 318 seconds at 100 F.

The test used involved immersing a 6 gram section of a cadmium-silver automobile bearing in a 30 gram sample of oil, heating the oil to a temperature of 175 C. and bubbling air therethrough against the surface of the bearing for a period of 22 hours. The loss in weight of the bearing section is a measure of the corrosion which has taken place.

Here again the trithioformaldehyde, probably because of low solubility, did not show material efi'ectiveness, but the trithioacetaldehyde when blended with this oil in the amount of 0.10 per cent reduced the loss in weight of the test specimen from-il mg. (for the oil alone) to 1 mg. (for the blend containing trithioacetaldehyde) It is to be understood that the terms highly refined, moderately refined and solvent-refined as used herein have reference to oils corresponding substantially in their manner of deterioration and inhibitor response to the examples given and are not necessarily restricted to oils obtained by particular refining operations. As has been previously pointed out, the final characteristics in an oil fraction are effected by the crude from which the oil is obtained as well as the refining treatment and by selection of the crude stock an oil of the highly refined type may be obtained by a treatment, which on another crude stock would yield an oil having the characteristics of a moderately refined oil.

The amount of the inhibitor used maybe varied, depending upon the oil fraction, from about 0.05 per cent to about 2.0 per cent more or less, depending upon its solubility-and whether an admixing solvent is employed. In general the amount satisfactory for substantial inhibition will be in the neighborhood of from about 0.05

per cent to about 0.1 per cent.

Iclaim:

1. A viscous mineral oil fraction having in admixture therewith a minor proportion of a thioaldehyde in an amount sumcient to inhibit the deleteriouseifects of oxidation on the oil.

' 2. An improved mineral oil composition comprising a highly refinedviscous mineral oil fraction and in admixture therewith a minor proportion of a thioaldehyde in an amount sufiicient to inhibit the deleterious effects of oxidation on the oil.

3. An improved mineral 'oil composition comprising a viscous mineral oil fraction and in admixture therewith a minor proportion of trithioacetaldehyde in an amount sufficient to inhibit the deleterious effects of oxidation on the oil.

4. An improved mineral oil composition comprising a. highly refined viscous mineral oil frac tion and in admixture therewith a minor proportion of a compound selected from the group consisting of trithioformaldehyde and trithioacetaldehyde, said compound being present in the oil in an amount sufllcient to inhibit the deleterious eflects of oxidation on the oil.

5. An improved mineral oil composition comprising a viscous mineral oil fraction having in admixture therewith a minor proportion of trithioformaldehyde in an amount sumcient to inhibit the deleterious efiects of oxidation on the oil.

6. An improved mineral oil composition comprising a viscous mineral oil fractionv selected from the group consisting of highly refined oils, moderately refined oils and solvent-refined oils, and in admixture therewith a minor proportion of trithioacetaldehyde in an amount suflicient to inhibit the deleterious effects of oxidation on the oil.

7. A viscous mineral oil fraction having in admixture-therewith a thioaldehyde in an amount of from about 0.05 per cent to about 0.1 per cent sufiicient toinhibit the deleterious efiects of oxidation on the oil.

8. An improved mineral oil composition comprising a viscous mineral oil fraction normally subject to deterioration under oxidizing conditions and in admixture therewith in minor proportion, sufilcient to retard said deterioration, a compound selected from the group consisting of trithioiormaldehyde and trithioacetaldehyde.

9. A viscous mineral oil fraction having in admixture therewith a minor proportion of an alkyl thioaldehyde in an amount suflicient to inhibit the deleterious efi'ects of oxidation. 

